New York City Mayor Bill de Blasio on Monday picked up the endorsement of Gov. Andrew Cuomo, his fellow Democrat and frequent political rival.

Gov. Cuomo voiced his support for the mayor during an interview on WNYC radio’s Brian Lehrer Show. Mayor De Blasio, who is seeking a second term, won last week’s five-way primary.

“The mayor won the Democratic primary. I am a Democrat,” Mr. Cuomo said while explaining his endorsement. “I support Democrats and I will support Mayor de Blasio in the general (election).”

Mr. Cuomo had declined to make an endorsement during the Democratic primary, saying it wasn’t his place as a resident of Westchester County, despite the fact that he’s endorsed candidates in other communities before.

The governor and Mr. de Blasio have feuded repeatedly, with Mr. Cuomo’s administration second-guessing the mayor and de Blasio complaining of Cuomo’s retaliation against his political opponents.

Asked Monday whether he was endorsing the mayor only out of party loyalty, Mr. Cuomo said no.

“In this contest, he is the better person to serve the city of New York as mayor, period,” he said.

Mayor De Blasio faces Republican state Assemblywoman Nicole Malliotakis of Staten Island in the November election.